No. A tiny square and a giant one cannot be congruent.
squares and triangles :/
Yes, a square will always be congruent, but rectangles also can be squares too. This is where you choose whether or not it is or not.
Squares and rhombuses can be congruent, but not always. If the rhombus is also a square, it is congruent to a square with the same dimensions. However, since a rhombus only demands for OPPOSITE angles to be congruent, and a square means ALL angles are 90 degrees, this is not always the case.
In a quadrilateral, the diagonals are only congruent for rectangles (or squares, which is a special kind of rectangle). Note: they are not congruent for a Rhombus.
Square and Rectangle
Squares and Rhombuses
Yes they are
Rectangles (including squares).
All rectangles, including squares.